Such an apparatus is known, comprising a heat exchanger having two opposed, parallel main faces and a bundle of tubes which extend parallel to the main faces and which are open into at least one water box of the heat exchanger, the apparatus further including a cooling fan arranged facing one of the main faces of the heat exchanger and in air communication with the tube bundle, with the cooling fan being arranged to rotate about an axis of rotation at right angles to the main faces whereby to produce a forced air stream through the heat exchanger, the apparatus also including a drive motor for driving the cooling fan, the motor and the cooling fan being secured to the heat exchanger. Such an apparatus will be referred to herein as apparatus of the kind specified.
In conventional apparatus of the kind specified, the drive motor is arranged on the same side of the heat exchanger as the cooling fan (i.e. it is associated with the same main face of the latter as the fan), the cooling fan being mounted directly on the output or drive shaft of the motor. This arrangement does have the advantage of simplifying the fitting of the motorised fan unit on the heat exchanger and to render superfluous any additional means for transmitting motion between the motor and the cooling fan. However, these advantages are more than offset by the following drawbacks. Firstly, the size of the drive motor in the axial direction is quite large, and adds to the overall thickness of the tube bundle. Secondly, the drive motor itself, and the means whereby it is fastened to the heat exchanger, tend to mask a not inconsiderable proportion of the exposed surface of the heat exchanger, thus reducing the cross section which is available for circulation of the air driven by the cooling fan. Thirdly, the drive motor and the cooling fan have to rotate at the same velocity as each other, even though, for optimum performance, they should rotate at different speeds. Finally, in the case in which the motorised fan unit lies downstream of the tube bundle of a cooling radiator (considered in the direction of flow of the forced air stream), the motor is in a draught of air which has already been heated by its contact with the tubes of the heat exchanger. This is detrimental to proper cooling of the motor itself.